The objectives of this study are: (1) to assess the progression of periodontal destruction among the cases of early onset periodontitis identified through the analysis of data from the 1986-1987 NIDR Survey of the Oral Health of U.S.A. Children, (2) characterize the microbial ecology of the subgingival plaque among persons with JP, (3) describe the periodontal destruction and presence of biologic and nonbiologic putative risk markers among the probands' similar aged siblings, and (4) compare the presence and concentration of selected putative pathogens, host-resistance factors, and non-biologic factors among individuals with and without JP, controlling for demographic or other characteristics which may confound the analysis if uncontrolled. Data sources include medical/dental histories, dental examinations, and samples of blood and subgingival plaque (collected with paper points and curettage). Immunological studies (serum antibodies and humoral immune response and neutrophil function) will be conducted on the blood samples; DNA probes for selected periopathogens will be conducted on the paper point samples; complete oral bacterial surveys will be done on the subgingival plaque samples collected by curettage (for a subset of cases and controls).